Processes using high resistive substrates (>50 Ohm-cm) need monitoring to ensure that a wafer meets design specifications and that an effective substrate resistance is maintained after fabrication without degrading the linear performance of active devices. Transmission lines, such as a coplanar waveguide, on a die are used as a monitor to determine whether the effective substrate resistance is maintained without degrading the linear performance of active devices. A coplanar waveguide (CPW) is formed from a conductor separated from a pair of ground planes all on the same plane, on a dielectric medium. The dielectric medium is thick enough so that electromagnetic fields fade out before they get out of the substrate. Active devices can be mounted on top of a circuit when using a CPW. More importantly, it can provide extremely high frequency response (100 GHz or more).
In addition, FET based switches are implemented in the die to study effects on the linear performance of the active devices. However, these monitors take up large amounts of die area. Furthermore, transmission lines placed on the die do not examine the non-linear performance of active devices, which is not known until their actual designs are tested. These monitors are tested using direct current (DC) and low frequency, e.g., 100 kilohertz, voltage supplies.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.